Electroluminescent device with quinazoline complex emitter

ABSTRACT

An OLED device comprises a cathode, an anode, and located therebetween a light-emitting layer containing a host material and a tris-ĈN-cyclometallated complex of Ir or Rh wherein at least one of the ligands comprises a substituted quinazoline moiety. The device provides useful emission and stability attributes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent is a continuation of commonly assigned, co-pending U.S. Ser.No. 11/289,023, filed Nov. 29, 2005, and published as U.S. 2007/0122655,which is incorporated herein by reference.

Reference is made to commonly assigned U.S. patent applications U.S.Ser. No. 10/945,337 filed Sep. 20, 2004 (now abandoned); U.S. Ser. No.11/016,134 filed Dec. 17, 2004 (now U.S. Pat. No. 7,579,090); U.S. Ser.No. 10/945,338 filed Sep. 20, 2004 (now abandoned); U.S. Ser. No.11/015,929 filed Dec. 17, 2004 (now U.S. Pat. No. 7,767,316), and U.S.Ser. No. 11/214,176, filed Aug. 29, 2005 (published as U.S.2007/0048544).

FIELD OF THE INVENTION

This invention relates to an organic light-emitting diode (OLED)electroluminescent (EL) device comprising a light-emitting layercontaining a host material and a phosphorescent light-emitting materialthat can provide desirable electroluminescent properties.

BACKGROUND OF THE INVENTION

While organic electroluminescent (EL) devices have been known for overtwo decades, their performance limitations have represented a barrier tomany desirable applications. In simplest form, an organic EL device iscomprised of an anode for hole injection, a cathode for electroninjection, and an organic medium sandwiched between these electrodes tosupport charge recombination that yields emission of light. Thesedevices are also commonly referred to as organic light-emitting diodes,or OLEDs. Representative of earlier organic EL devices are Gurnee et al.U.S. Pat. No. 3,172,862, issued Mar. 9, 1965; Gurnee U.S. Pat. No.3,173,050, issued Mar. 9, 1965; Dresner, “Double InjectionElectroluminescence in Anthracene”, RCA Review, Vol. 30, pp. 322-334,1969; and Dresner et al. U.S. Pat. No. 3,710,167, issued Jan. 9, 1973.The organic layers in these devices, usually composed of a polycyclicaromatic hydrocarbon, were very thick (much greater than 1 μm).Consequently, operating voltages were very high, often >100V.

More recent organic EL devices include an organic EL element consistingof extremely thin layers (e.g. <1.0 μm) between the anode and thecathode. Herein, the term “organic EL element” encompasses the layersbetween the anode and cathode electrodes. Reducing the thickness loweredthe resistance of the organic layer and has enabled devices that operatemuch lower voltage. In a basic two-layer EL device structure, describedfirst in U.S. Pat. No. 4,356,429, one organic layer of the EL elementadjacent to the anode is specifically chosen to transport holes,therefore, it is referred to as the hole-transporting layer, and theother organic layer is specifically chosen to transport electrons,referred to as the electron-transporting layer. Recombination of theinjected holes and electrons within the organic EL element results inefficient electroluminescence.

There have also been proposed three-layer organic EL devices thatcontain an organic light-emitting layer (LEL) between thehole-transporting layer and electron-transporting layer, such as thatdisclosed by Tang et al. [J. Applied Physics, Vol. 65, pp. 3610-3616,1989]. The light-emitting layer commonly consists of a host materialdoped with a guest material. Still further, there has been proposed inU.S. Pat. No. 4,769,292 a four-layer EL element comprising ahole-injecting layer (HIL), a hole-transporting layer (HTL), alight-emitting layer (LEL) and an electron transport/injection layer(ETL). These structures have resulted in improved device efficiency.

Many emitting materials that have been described as useful in an OLEDdevice emit light from their excited singlet state by fluorescence. Theexcited singlet state is created when excitons formed in an OLED devicetransfer their energy to the excited state of the dopant. However, it isgenerally believed that only 25% of the excitons created in an EL deviceare singlet excitons. The remaining excitons are triplet, which cannotreadily transfer their energy to the singlet-excited state of a dopant.This results in a large loss in efficiency since 75% of the excitons arenot used in the light emission process.

Triplet excitons can transfer their energy to a dopant if it has atriplet excited state that is low enough in energy. If the triplet stateof the dopant is emissive, it can produce light by phosphorescence. Inmany cases, singlet excitons can also transfer their energy to lowestsinglet excited state of the same dopant. The singlet excited state canoften relax, by an intersystem crossing process, to the emissive tripletexcited state. Thus, it is possible, by the proper choice of host anddopant, to collect energy from both the singlet and triplet excitonscreated in an OLED device and to produce a very efficient phosphorescentemission.

Singlet and triplet states, fluorescence, phosphorescence, andintersystem crossing are discussed in J. G. Calvert and J. N. Pitts,Jr., Photochemistry (Wiley, New York, 1966). Emission from tripletstates is generally very weak for most organic compounds because thetransition from triplet-excited state to singlet ground state isspin-forbidden. However, it is possible for compounds with statespossessing a strong spin-orbit coupling interaction to emit stronglyfrom triplet-excited states to the singlet ground state(phosphorescence). One such strongly phosphorescent compound isfac-tris(2-phenyl-pyridinato-N̂C-)Iridium(III) (Ir(ppy)₃) that emitsgreen light (K. A. King, P. J. Spellane, and R. J. Watts, J. Am. Chem.Soc., 107, 1431 (1985), M. G. Colombo, T. C. Brunold, T. Reidener, H. U.Giidel, M. Fortsch, and H.-B. Bürgi, Inorg. Chem., 33, 545 (1994)).Organic electroluminescent devices having high efficiency have beendemonstrated with Ir(ppy)₃ as the phosphorescent material and4,4′-N,N′-dicarbazole-biphenyl (CBP) as the host (M. A. Baldo, S.Lamansky, P. E. Burrows, M. E. Thompson, S. R. Forrest, Appl. Phys.Lett., 75, 4 (1999), T. Tsutsui, M.-J. Yang, M. Yahiro, K. Nakamura, T.Watanabe, T. Tsuji, Y. Fukuda, T. Wakimoto, S. Miyaguchi, Jpn. J. Appl.Phys., 38, L1502 (1999)). Additional disclosures of phosphorescentmaterials and organic electroluminescent devices employing thesematerials are found in U.S. Pat. No. 6,303,238 B1, WO 00/57676, WO00/70655, and WO 01/41512 A1.

There is a continuing need to develop new phosphorescent materials forimproved stability and to provide a wide range of hues. S. Seo andco-workers, SID 05 Digest, 806 (2005), Y. Chi et al., Inorg. Chem., 44,1344 (2005), C. Chen et al., Adv. Funct. Mater., 14, 1221 (2004), and C.Cheng et al., Adv. Mater., 15, 224 (2003) describe iridium complexesthat include two ĈN-cyclometallated quinazoline ligands and oneancillary ligand. The ancillary ligand is an anionic bidentate ligandthat does not provide a carbon bonded to Ir. Although these materialsare reported to have interesting properties it is generally the casethat bis-cyclometallated metal complexes, although easier to synthesize,are less stable relative to tris-ĈN-cyclometallated metal complexes.

Fujii et al, U.S. 2005/0191527, describes organometallic compounds withquinoxaline ligands including tris-ĈN-cyclometallated complexes ofiridium. Mishima et al., U.S. 2005/0191519, describes triplet emitterswith various heterocyclic ligands. Some of these complexes are alsotris-ĈN-cyclometallated complexes of iridium, although none of thetris-ĈN-cyclometallated complexes include a quinazoline ligand. However,many of the materials described in these disclosures emit at wavelengthsthat are too deep to be useful in a practical OLED device.

The nature of the host material is also critical to get good performancefrom the phosphorescent emitter. For example, U.S. Ser. Nos. 10/945,337and 10/945,338 filed Sep. 20, 2004 (both now abandoned), and U.S. Ser.Nos. 11/015,929 and 11/016,134 filed Dec. 17, 2004 (now U.S. Pat. Nos.7,767,316 and 7,579,090 respectively), describe an EL device in whichthe light-emitting layer includes a hole-transporting compound, certainaluminum chelate materials, and a light-emitting phosphorescentcompound. U.S. Ser. No. 11/214,176 filed Aug. 29, 2005 (published asU.S. 2007/0048544), describes an EL device in which the light-emittinglayer includes a hole-transporting compound, certain gallium chelatematerials, and a light-emitting phosphorescent compound.

Notwithstanding these developments, there remains a need for newphosphorescent materials to provide useful emission and stabilityattributes

SUMMARY OF THE INVENTION

The invention provides an OLED device that comprises a cathode, ananode, and located therebetween a light-emitting layer containing a hostmaterial and a tris-ĈN-cyclometallated complex of Ir or Rh wherein atleast one of the ligands comprises a substituted quinazoline moiety. Thedevice provides useful emission and stability attributes.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows a schematic cross-sectional view of one embodiment ofthe device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The organic light-emitting device (OLED) of the invention contains acathode, a light-emitting layer, and an anode as described above. Thelight-emitting layer includes a host material and atris-ĈN-cyclometallated complex of Ir or Rh wherein at least one of theligands comprises a substituted quinazoline moiety. A quinazolinenucleus and its ring-numbering is shown below.

Desirably, the metal forms a nitrogen-metal bond with one nitrogen ofthe quinazoline nucleus, and forms a carbon-metal bond with asubstituent on the quinazoline nucleus. Suitably, the substituent is atthe 2 or the 4 position and includes at least one carbon-carbon doublebond, and the metal is bonded to one carbon of the double bond.Desirably the substituent is an aromatic group, such as a phenyl group,naphthyl group, or thienyl group.

The metal is Ir or Rh. Desirably the metal is Ir. In one embodiment thecomplex includes three independently selected substituted quinazolinemoieties, and the metal is bonded to each of these moieties as describedabove.

In another embodiment, the substituted quinazoline moiety is a2-phenylquinazoline group or a 4-phenylquinazoline group. In a similarembodiment, the complex includes three independently selected2-phenylquinazoline groups or 4-phenylquinazoline groups.

The tris-ĈN-cyclometallated complex may be a facial or a meridionalisomer. Desirably the complex is a facial isomer, since they are oftenfound to have higher emission quantum yield than the meridional isomer.

In another aspect of the invention, the tris-ĈN-cyclometallated complexis represented by Formula (1a) or Formula (1b).

In Formulae (1a) and (1b), M represents Ir or Rh. Each R¹-R⁷ representshydrogen or an independently selected substituent group such as a phenylgroup, a methyl group, or a trifluoromethyl group. Two of R¹-R⁷ maycombine to form a ring group, such as a fused benzene ring group. In onedesirable embodiment R⁶ and R⁷ combine to form an aromatic group, suchas a benzene group or thiophene group. In another embodiment, two ofR¹-R⁵ do not combine to form a fused ring, and thus the quinazolinenucleus does not have additional fused rings.

In Formulae (1a) and (1b), A represents a substituted or unsubstitutedheterocyclic ring group containing at least one nitrogen atom, such as apyridine ring group, a pyrazole ring group, an isoquinoline ring group,or a quinoline ring group.

In the Formulae, B represents a substituted or unsubstituted aromatic orheteroaromatic ring. Examples of B include a phenyl ring group, a4,6-difluorophenyl ring group, and a thienyl ring group. In one suitableembodiment, B represents an aryl group.

In the Formulae, m is an integer from 1 to 3; and n is an integer from 0to 2 such that m+n=3. In one desirable embodiment, m is 3 and n is 0.

In a further aspect of the invention, the metal complex is representedby Formula (2a) or Formula (2b).

In Formulae (2a) and (2b), M and R¹-R⁷ have been described previously.In one desirable embodiment, R⁶ and R⁷ combine to form an aromatic ring.

In a another aspect of the invention, the metal complex is representedby (2c) or (2d):

In Formula (2c) and (2d), each d¹ and each d² represent independentlyselected substituents, such as a phenyl group or methyl group.Preferably, adjacent substituents do not combine to form a fused ring.

In Formula (2c) and (2d), s is 0-4, t is 0-4, and d³ represents hydrogenor a substituent.

Tris-ĈN-cyclometallated complexes of iridium and rhodium may besynthesized by methods described in the literature. However, it is oftenfound that many of the methods are not generally applicable and work foronly limited types of ĈN-cyclometallating ligands. Through diligentexperimentation in the synthetic methodology fortris-ĈN-cyclometallating iridium complexes, the inventors have now foundthat the method recently disclosed in U.S. Ser. No. 10/879,657, filedJun. 29, 2004, now U.S. Pat. No. 7,005,522, results in efficientsynthesis of the tris-ĈN-cyclometallated complexes of the presentinvention having ligands that N-coordinate through quinazoline moieties.For cases of tris-ĈN-cyclometallated complexes where the threeĈN-cyclometallating ligands are not all the same, the methods describedin U.S. Pat. No. 6,835,835, U.S. Ser. Nos. 11/015,910, 11/134,120 (nowU.S. Pat. Nos. 7,417,146 and 7,476,739 respectively), and U.S. Ser. No.11/240,288 filed Sep. 30, 2005 (now U.S. Pat. No. 7,517,984) may beused.

Illustrative examples of Formula (1) and Formula (2) compounds arelisted below.

The light-emitting layer also includes at least one host material.Desirably the host material has a triplet energy higher than or equal tothe triplet energy of the metal complex. Triplet energy is convenientlymeasured by any of several means, as discussed for instance in S. L.Murov, I. Carmichael, and G. L. Hug, Handbook of Photochemistry, 2nd ed.(Marcel Dekker, New York, 1993).

In the absence of experimental data the triplet energies may beestimated in the following manner. The triplet state energy for amolecule is defined as the difference between the ground state energy(E(gs)) of the molecule and the energy of the lowest triplet state(E(ts)) of the molecule, both given in eV. These energies can becalculated using the B3LYP method as implemented in the Gaussian98(Gaussian, Inc., Pittsburgh, Pa.) computer program. The basis set foruse with the B3LYP method is defined as follows: MIDI! for all atoms forwhich MIDI! is defined, 6-31G* for all atoms defined in 6-31G* but notin MIDI!, and either the LACV3P or the LANL2DZ basis set andpseudopotential for atoms not defined in MIDI! or 6-31G*, with LACV3Pbeing the preferred method. For any remaining atoms, any published basisset and pseudopotential may be used. MIDI!, 6-31G* and LANL2DZ are usedas implemented in the Gaussian98 computer code and LACV3P is used asimplemented in the Jaguar 4.1 (Schrodinger, Inc., Portland, Oreg.)computer code. The energy of each state is computed at theminimum-energy geometry for that state. The difference in energy betweenthe two states is further modified by Equation 1 to give the tripletstate energy (E(t)):

E(t)=0.84*(E(ts)−E(gs))+0.35  (1)

For polymeric or oligomeric materials, it is sufficient to compute thetriplet energy over a monomer or oligomer of sufficient size so thatadditional units do not substantially change the computed triplet energyof the material.

Suitable host materials should be selected so that the triplet excitoncan be transferred efficiently from the host material to thephosphorescent material. For this transfer to occur, it is a highlydesirable condition that the excited state energy of the phosphorescentmaterial be lower than the difference in energy between the lowesttriplet state and the ground state of the host, although efficientemission has been reported for devices where the host has a lowertriplet energy than the dopant by M. A. Baldo, M. E. Thompson, S. K.Forrest, and co-workers, Appl. Phys. Lett., 79, 2082 (2001). However,the band gap of the host should not be chosen so large as to cause anunacceptable increase in the drive voltage of the OLED. Suitable hostmaterials are described in WO 00/70655, WO 01/39234, WO 01/93642, WO02/074015, WO 02/15645, and U.S. 2002/0117662. Suitable hosts includecertain aryl amines, triazoles, indoles, and carbazole compounds.Examples of desirable hosts are 4,4′-N,N′-dicarbazole-biphenyl (CBP),2,2′-dimethyl-4,4′-N,N′-dicarbazole-biphenyl,m-(N,N′-dicarbazole)benzene, and poly(N-vinylcarbazole), including theirderivatives. In one embodiment, the host material includes a carbazolederivative.

Types of triplet host materials may be categorized according to theircharge transport properties. The two major types are those that arepredominantly electron transporting and those that are predominantlyhole transporting. It should be noted that some host materials, whichmay be categorized as transporting dominantly one type of charge, maytransport both types of charges, especially in certain devicestructures, for example CBP which is described in C. Adachi, R. Kwong,and S. R. Forrest, Organic Electronics, 2, 37-43 (2001). Another type ofhost are those having a wide energy gap between the HOMO and LUMO, suchthat they do not readily transport charges of either type, and insteadrely on charge injection directly into the phosphorescent dopantmolecules.

A desirable electron-transporting host may be any suitableelectron-transporting compound, such as benzazole, phenanthroline,1,3,4-oxadiazole, triazole, triazine, or triarylborane, as long as ithas a triplet energy that is higher than that of the phosphorescentemitter to be employed.

A preferred class of benzazoles is described by Jianmin Shi et al. inU.S. Pat. Nos. 5,645,948 and 5,766,779. Such compounds are representedby structural formula (PHF-1):

-   -   In formula (PHF-1),

n is selected from 2 to 8;

Z is independently O, NR or S;

R and R′ are individually hydrogen; alkyl of from 1 to 24 carbon atoms,for example, propyl, t-butyl, heptyl, and the like; aryl or hetero-atomsubstituted aryl of from 5 to 20 carbon atoms, for example, phenyl andnaphthyl, furyl, thienyl, pyridyl, quinolinyl, and other heterocyclicsystems; or halo such as chloro, fluoro; or atoms necessary to completea fused aromatic ring; and

X is a linkage unit consisting of carbon, alkyl, aryl, substitutedalkyl, or substituted aryl, which conjugately or unconjugately connectsthe multiple benzazoles together.

An example of a useful benzazole is2,2′,2″-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole] (TPBI)represented by a formula (PHF-2) shown below:

Another class of electron-transporting materials suitable for use as ahost includes various substituted phenanthrolines as represented byformula (PHF-3):

In formula (PHF-3), R₁-R₈ are independently hydrogen, alkyl group, aryl,or substituted aryl group, and at least one of R₁-R₈ is aryl group orsubstituted aryl group.

Examples of suitable materials are2,9-dimethyl-4,7-diphenyl-phenanthroline (BCP) (see formula (PH-1)) and4,7-diphenyl-1,10-phenanthroline (Bphen) (see formula (PH-2)).

A triarylborane that functions as an electron-transporting host may beselected from compounds having the chemical formula (PHF-4):

wherein Ar₁ to Ar₃ are independently an aromatic hydrocarbocyclic groupor an aromatic heterocyclic group, which may have one or moresubstituent.

It is preferable that compounds having the above structure are selectedfrom formula (PHF-5):

wherein R₁-R₁₅ are independently hydrogen, fluoro, cyano,trifluoromethyl, sulfonyl, alkyl, aryl, or substituted aryl group.

Specific representative embodiments of the triarylboranes include:

An electron-transporting host may be selected from substituted1,3,4-oxadiazoles. Illustrative of the useful substituted oxadiazolesare the following:

An electron-transporting host may be selected from substituted1,2,4-triazoles. An example of a useful triazole is3-phenyl-4-(1-naphthyl)-5-phenyl-1,2,4-triazole represented by formula(PHF-6):

The electron-transporting host may be selected from substituted1,3,5-triazines. Examples of suitable materials are:

-   2,4,6-tris(diphenylamino)-1,3,5-triazine;-   2,4,6-tricarbazolo-1,3,5-triazine;-   2,4,6-tris(N-phenyl-2-naphthylamino)-1,3,5-triazine;-   2,4,6-tris(N-phenyl-1-naphthylamino)-1,3,5-triazine;-   4,4′,6,6′-tetraphenyl-2,2′-bi-1,3,5-triazine;-   2,4,6-tris([1,1′:3′,1″-terphenyl]-5′-yl)-1,3,5-triazine.

In one embodiment, the host material includes a material that is analuminum or gallium complex. Particularly useful host materials arerepresented by Formula (PHF-7) also referred to herein as Formula (3).

In Formula (3), M₁ represents Al or Ga. R₂-R₇ represent hydrogen or anindependently selected substituent. Desirably, R₂ represents anelectron-donating group, such as a methyl group. Suitably, R₃ and R₄each independently represent hydrogen or an electron-donatingsubstituent. Preferably, R₅, R₆, and R₇ each independently representhydrogen or an electron-accepting group. Adjacent substituents, R₂-R₇,may combine to form a ring group. L is an aromatic moiety linked to thealuminum by oxygen, which may be substituted with substituent groupssuch that L has from 6 to 30 carbon atoms. Illustrative examples ofFormula (3) materials are listed below.

A suitable class of hole-transporting compounds for use as a host arearomatic tertiary amines, by which it is understood to be compoundscontaining at least one trivalent nitrogen atom that is bonded only tocarbon atoms, at least one of which is a member of an aromatic ring. Inone form the aromatic tertiary amine can be an arylamine, such as amonoarylamine, diarylamine, triarylamine, or a polymeric arylamine.Exemplary monomeric triarylamines are illustrated by Klupfel et al. inU.S. Pat. No. 3,180,730. Other suitable triarylamines substituted withone or more vinyl radicals and/or comprising at least one activehydrogen containing group are disclosed by Brantly et al. in U.S. Pat.Nos. 3,567,450 and 3,658,520.

A more preferred class of aromatic tertiary amines are those whichinclude at least two aromatic tertiary amine moieties as described inU.S. Pat. Nos. 4,720,432 and 5,061,569, such as the tetraaryldiamines.Desirable tetraaryldiamines include two diarylamino groups, such asindicated by formula (PHF-8):

wherein:

each Are is an independently selected arylene group, such as a phenyleneor anthracene moiety,

n is selected from 1 to 4, and

R₁-R₄ are independently selected aryl groups.

In a typical embodiment, at least one of R₁-R₄ is a polycyclic fusedring structure, e.g., a naphthalene. However, when the emission of thedopant is blue or green in color it is less preferred for the hostmaterial to have a polycyclic fused ring substituent.

Representative examples of the useful compounds include the following:

-   4,4′-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB);-   4,4′-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl (TNB);-   4,4′-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD);-   4,4′-Bis-diphenylamino-terphenyl;-   2,6,2′,6′-tetramethyl-N,N,N′,N′-tetraphenyl-benzidine.4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine    (MTDATA);-   4,4′,4″-tris(N,N-diphenyl-amino)triphenylamine (TDATA);-   N,N-bis[2,5-dimethyl-4-[(3-methylphenyl)phenylamino]phenyl]-2,5-dimethyl-N′-(3-methylphenyl)-N′-phenyl-1,4-benzenediamine.

In one desirable embodiment the hole-transporting host comprises amaterial of formula (PHF-9):

In formula (PHF-9),

R₁ and R₂ represent substituents, provided that R₁ and R₂ can join toform a ring. For example, R₁ and R₂ can be methyl groups or can join toform a cyclohexyl ring;

Ar₁-Ar₄ represent independently selected aromatic groups, for examplephenyl groups or tolyl groups;

R₃-R₁₀ independently represent hydrogen, alkyl, substituted alkyl, aryl,substituted aryl group.

Examples of suitable materials include, but are not limited to:

-   1,1-Bis(4-(N, N-di-p-tolylamino)phenyl)cyclohexane (TAPC);-   1,1-Bis(4-(N, N-di-p-tolylamino)phenyl)cyclopentane;-   4,4′-(9H-fluoren-9-ylidene)bis[N,N-bis(4-methylphenyl)-benzenamine;-   1,1-Bis(4-(N, N-di-p-tolylamino)phenyl)-4-phenylcyclohexane;-   1,1-Bis(4-(N, N-di-p-tolylamino)phenyl)-4-methylcyclohexane;-   1,1-Bis(4-(N, N-di-p-tolylamino)phenyl)-3-phenylpropane;-   Bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylpenyl)methane;-   Bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)ethane;-   4-(4-Diethylaminophenyl)triphenylmethane;-   4,4′-Bis(4-diethylaminophenyl)diphenylmethane.

A useful class of compounds for use as the hole-transporting hostincludes carbazole derivatives such as those represented by formula(PHF-10):

In formula (PHF-10),

Q independently represents nitrogen, carbon, silicon, a substitutedsilicon group, an aryl group, or substituted aryl group, preferably aphenyl group;

R₁ is preferably an aryl or substituted aryl group, and more preferablya phenyl group, substituted phenyl, biphenyl, or substituted biphenylgroup;

R₂ through R₇ are independently hydrogen, alkyl, phenyl or substitutedphenyl group, aryl amine, carbazole, or substituted carbazole;

and n is selected from 1 to 4.

Illustrative useful substituted carbazoles are the following:

-   4-(9H-carbazol-9-yl)-N,N-bis[4-(9H-carbazol-9-yl)phenyl]-benzenamine    (TCTA);-   4-(3-phenyl-9H-carbazol-9-yl)-N,N-bis[4(3-phenyl-9H-carbazol-9-yl)phenyl]-benzenamine;-   9,9′-[5′-[4-(9H-carbazol-9-yl)phenyl][1,1′:3′,1″-terphenyl]-4,4″-diyl]bis-9H-carbazole.-   3,5-bis(9-carbazolyl)tetraphenylsilane (SimCP).

In one suitable embodiment the hole-transporting host comprises amaterial of formula (PHF-11):

In formula (PHF-11),

n is selected from 1 to 4;

Q independently represents phenyl group, substituted phenyl group,biphenyl, substituted biphenyl group, aryl, or substituted aryl group;

R₁ through R₆ are independently hydrogen, alkyl, phenyl or substitutedphenyl, aryl amine, carbazole, or substituted carbazole.

Examples of suitable materials are the following:

-   9,9′-(2,2′-dimethyl[1,1′-biphenyl]-4,4′-diyl)bis-9H-carbazole    (CDBP);-   9,9′[1,1′-biphenyl]-4,4′-diylbis-9H-carbazole (CBP);-   9,9′-(1,3-phenylene)bis-9H-carbazole (mCP);-   9,9′-(1,4-phenylene)bis-9H-carbazole;-   9,9′,9″-(1,3,5-benzenetriyl)tris-9H-carbazole;-   9,9′-(1,4-phenylene)bis[N,N,N′,N′-tetraphenyl-9H-carbazole-3,6-diamine;-   9-[4-(9H-carbazol-9-yl)phenyl]-N,N-diphenyl-9H-carbazol-3-amine;-   9,9′-(1,4-phenylene)bis[N,N-diphenyl-9H-carbazol-3-amine;-   9-[4-(9H-carbazol-9-yl)phenyl]-N,N,N′,N′-tetraphenyl-9H-carbazole-3,6-diamine.

Host materials that are electron-transporting or hole-transporting withsome electron-transporting properties, such as carbazoles, are generallymore desirable when used as a single host material. This is especiallytrue for typical phosphorescent dopants that are hole-trapping or arecapable of accepting injected holes. Less preferable are host materialsthat are primarily hole transporting and have littleelectron-transporting properties, such as triarlyamines. Injectingelectrons into these latter hole-transporting hosts may be difficultbecause of their relatively high LUMO energies.

Host materials may comprise a mixture of two or more host materials.Particularly useful is a mixture comprising at least one each of anelectron-transporting and a hole-transporting co-host. The optimumconcentration of the hole-transporting co-host(s) may be determined byexperimentation and may be within the range 5 to 60 volume % of thetotal of the hole- and electron-transporting co-host materials in thelight-emitting layer, and is often found to be in the range 15 to 30vol. %. It is further noted that electron-transporting molecules andhole-transporting molecules may be covalently joined together to formsingle host molecules having both electron-transporting andhole-transporting properties.

In one aspect of the invention, the host material of the light-emittinglayer includes a host of Formula (3) and at least one additional hostcompound, also referred to as a co-host, is present. Desirably theco-host is a compound capable of transporting holes.

The co-host having hole-transporting properties may be any suitablehole-transporting compound, such as a triarylamine or carbazole, as longit has a triplet energy that is higher than that of the phosphorescentdopant to be employed. The optimum concentration of thehole-transporting co-host relative to the host of Formula (3) in thepresent invention may be determined by experimentation. Theconcentration of the hole-transporting co-host is frequently within therange 5 to 60% of the light-emitting layer by volume, and is often foundto be in the range 10 to 30%, or commonly in the range of 10 to 20%.

In one desirable embodiment, the co-host is represented by Formula (4).

In Formula (4),

each Ar^(a) and each Ar^(b) may be the same or different and eachindependently represents an aromatic group, such as a phenyl group or anaphthyl group;

each R^(a) and each R^(b) may be the same or different and eachindependently represents a substituent group; and

n and m independently are 0-4. In one suitable embodiment, n is 0 and mis 0.

A wide energy gap host material may be any suitable compound having alarge HOMO-LUMO gap such that the HOMO and LUMO of the phosphorescentemissive material are within the HOMO and LUMO for the host. In thiscase, the phosphorescent emissive material acts as the primary chargecarrier for both electrons and holes, as well as the site for thetrapping of excitons. Often the phosphorescent dopants for use with thewide energy gap hosts are selected to have electron-withdrawingsubstituents to facilitate electron injection. The “wide energy gap”host material functions as a non-charge carrying material in the system.Such a combination may lead to high operation voltage of the device, asthe concentration of the charge-carrying dopant is typically below 10%in the emissive layer.

Thompson et al. disclosed in U.S. 2004/0209115 and U.S. 2004/0209116 agroup of wide energy gap hosts having triplet energies suitable for bluephosphorescent OLEDs. Such compounds include those represented bystructural formula (PHF-12):

wherein:

X is Si or Pb; and

Ar₁, Ar₂, Ar₃, and Ar₄ are each an aromatic group independently selectedfrom phenyl and high triplet energy heterocyclic groups such aspyridine, pyrazole, thiophene, etc.

It is believed that the HOMO-LUMO gaps in these materials are large dueto the electronically isolated aromatic units and the lack of anyconjugating substituents.

Illustrative examples of this type of hosts include:

In many known hosts and device architectures for phosphorescent OLEDs,the optimum concentration of the phosphorescent dopant for luminousefficiency is found to be about 1 to 20 vol. % and often 6 to 8 vol. %relative to the host material. In one aspect of the invention, wherein amixture of an electron-transporting host and a hole-transporting co-hostis present in the light-emitting layer, a phosphorescent materialconcentration from about 0.5% to about 6% often provides high luminousefficiencies.

In addition to suitable hosts, an EL device employing a phosphorescentmaterial often is more efficient if there is at least one exciton- orhole-blocking layer on the cathode side of the emitting layer.Efficiency can also often be improved if there are one or more exciton-or electron-blocking layers on the anode side of the emitting layer.These additional layers help confine the excitons or electron-holerecombination centers to the light-emitting layer comprising the hostand emitting material.

An exciton- or hole-blocking layer is desirably placed between theelectron-transporting layer and the light-emitting layer, Layer 109 inthe FIGURE. The ionization potential of the blocking layer should besuch that there is an energy barrier for hole migration from the hostinto the electron-transporting layer, while the electron affinity shouldbe such that electrons pass more readily from the electron-transportinglayer into the light-emitting layer comprising host and phosphorescentmaterial. It is further desired, but not absolutely required, that thetriplet energy of the blocking material be greater than that of thephosphorescent material. Suitable hole-blocking materials are describedin WO 00/70655 A2 and WO 01/93642 A1. Two examples of useful materialsare bathocuproine (BCP) andbis(2-methyl-8-quinolinolato)(4-phenylphenolato)Aluminum(III) (BAlq).Metal complexes other than BAlq are also known to block holes andexcitons as described in U.S. 2003/0068528. Depending on the nature ofthe electron-transporting material and the configuration of the LEL,this blocking layer, in certain cases, can be entirely omitted.

In another embodiment, an exciton- or electron-blocking layer would beplaced between the hole-transporting layer and the light-emitting layer(this layer is not shown in the FIGURE). As an example, U.S.2003/0175553 describes the use offac-tris(1-phenylpyrazolato-N,C^(2′))iridium(III) (Ir(ppz)₃) in anelectron-/exciton-blocking layer. U.S. Ser. No. 11/016,108 of Marina E.Kondakova et al., filed Dec. 17, 2004 (now U.S. Pat. No. 7,597,967),describes further examples of exciton-blocking layers. Depending on thenature of the hole-transporting material and the configuration of theLEL, this blocking layer, in certain cases, can be entirely omitted.

Unless otherwise specifically stated, use of the term “substituted” or“substituent” means any group or atom other than hydrogen. Unlessotherwise provided, when a group, compound, or formula containing asubstitutable hydrogen is referred to, it is also intended to encompassnot only the substituent's unsubstituted form, but also its form furthersubstituted with any substituent group or groups as herein mentioned, solong as the substituent does not destroy properties necessary for deviceutility. Suitably, a substituent group may be halogen or may be bondedto the remainder of the molecule by an atom of carbon, silicon, oxygen,nitrogen, phosphorous, sulfur, selenium, or boron. The substituent maybe, for example, halogen, such as chloro, bromo or fluoro; nitro;hydroxyl; cyano; carboxyl; or groups which may be further substituted,such as alkyl, including straight or branched chain or cyclic alkyl,such as methyl, trifluoromethyl, ethyl, t-butyl,3-(2,4-di-t-pentylphenoxy) propyl, and tetradecyl; alkenyl, such asethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy,2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy, tetradecyloxy,2-(2,4-di-t-pentylphenoxy)ethoxy, and 2-dodecyloxyethoxy; aryl such asphenyl, 4-t-butylphenyl, 2,4,6-trimethylphenyl, naphthyl; aryloxy, suchas phenoxy, 2-methylphenoxy, alpha- or beta-naphthyloxy, and 4-tolyloxy;carbonamido, such as acetamido, benzamido, butyramido, tetradecanamido,alpha-(2,4-di-t-pentyl-phenoxy)acetamido,alpha-(2,4-di-t-pentylphenoxy)butyramido,alpha-(3-pentadecylphenoxy)-hexanamido,alpha-(4-hydroxy-3-t-butylphenoxy)-tetradecanamido,2-oxo-pyrrolidin-1-yl, 2-oxo-5-tetradecylpyrrolin-l-yl,N-methyltetradecanamido, N-succinimido, N-phthalimido,2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo-1-imidazolyl, andN-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino,benzyloxycarbonylamino, hexadecyloxycarbonylamino,2,4-di-t-butylphenoxycarbonyl-amino, phenylcarbonylamino,2,5-(di-t-pentylphenyl)carbonylamino, p-dodecyl-phenylcarbonylamino,p-tolylcarbonylamino, N-methylureido, N,N-dimethylureido,N-methyl-N-dodecylureido, N-hexadecylureido, N,N-dioctadecylureido,N,N-dioctyl-N′-ethylureido, N-phenylureido, N,N-diphenylureido,N-phenyl-N-p-tolylureido, N-(m-hexadecylphenyl)ureido,N,N-(2,5-di-t-pentylphenyl)-N′-ethylureido, and t-butylcarbonamido;sulfonamido, such as methylsulfonamido, benzenesulfonamido,p-tolylsulfonamido, p-dodecylbenzenesulfonamido,N-methyltetradecylsulfonamido, N,N-dipropyl-sulfamoylamino, andhexadecylsulfonamido; sulfamoyl, such as N-methylsulfamoyl,N-ethylsulfamoyl, N,N-dipropylsulfamoyl, N-hexadecylsulfamoyl,N,N-dimethylsulfamoyl, N-[3-(dodecyloxy)propyl]sulfamoyl,N-[4-(2,4-di-t-pentylphenoxy)butyl]sulfamoyl,N-methyl-N-tetradecylsulfamoyl, and N-dodecylsulfamoyl; carbamoyl, suchas N-methylcarbamoyl, N,N-dibutylcarbamoyl, N-octadecylcarbamoyl,N-[4-(2,4-di-t-pentylphenoxy)butyl]carbamoyl,N-methyl-N-tetradecylcarbamoyl, and N,N-dioctylcarbamoyl; acyl, such asacetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl,p-dodecyloxyphenoxycarbonyl methoxycarbonyl, butoxycarbonyl,tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl,3-pentadecyloxycarbonyl, and dodecyloxycarbonyl; sulfonyl, such asmethoxysulfonyl, octyloxysulfonyl, tetradecyloxysulfonyl,2-ethylhexyl-oxysulfonyl, phenoxysulfonyl,2,4-di-t-pentylphenoxysulfonyl, methylsulfonyl, octylsulfonyl,2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl,phenylsulfonyl, 4-nonylphenylsulfonyl, and p-tolylsulfonyl; sulfonyloxy,such as dodecylsulfonyloxy, and hexadecylsulfonyloxy; sulfinyl, such asmethylsulfinyl, octylsulfinyl, 2-ethylhexylsulfinyl, dodecylsulfinyl,hexadecylsulfinyl, phenylsulfinyl, 4-nonylphenylsulfinyl, andp-tolylsulfinyl; thio, such as ethylthio, octylthio, benzylthio,tetradecylthio, 2-(2,4-di-t-pentylphenoxy)ethylthio, phenylthio,2-butoxy-5-t-octylphenylthio, and p-tolylthio; acyloxy, such asacetyloxy, benzoyloxy, octadecanoyloxy, p-dodecylamidobenzoyloxy,N-phenylcarbamoyloxy, N-ethylcarbamoyloxy, and cyclohexylcarbonyloxy;amine, such as phenylanilino, 2-chloroanilino, diethylamine,dodecylamine; imino, such as 1 (N-phenylimido)ethyl, N-succinimido or3-benzylhydantoinyl; phosphate, such as dimethylphosphate andethylbutylphosphate; phosphite, such as diethyl and dihexylphosphite; aheterocyclic group, a heterocyclic oxy group or a heterocyclic thiogroup, each of which may be substituted and which contain a 3 to 7membered heterocyclic ring composed of carbon atoms and at least onehetero atom selected from the group consisting of oxygen, nitrogen,sulfur or phosphorus, such as pyridyl, thienyl, furyl, azolyl,thiazolyl, oxazolyl, imidazolyl, pyrazolyl, pyrazinyl, pyrimidinyl,pyrolidinonyl, quinolinyl, isoquinolinyl, 2-furyl, 2-thienyl,2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such astriethylammonium; quaternary phosphonium, such as triphenylphosphonium;and silyloxy, such as trimethylsilyloxy.

If desired, the substituents may themselves be further substituted oneor more times with the described substituent groups. The particularsubstituents used may be selected by those skilled in the art to attaindesirable properties for a specific application and can include, forexample, electron-withdrawing groups, electron-donating groups, andsteric groups. When a molecule may have two or more substituents, thesubstituents may be joined together to form a ring such as a fused ringunless otherwise provided. Generally, the above groups and substituentsthereof may include those having up to 48 carbon atoms, typically 1 to36 carbon atoms and usually less than 24 carbon atoms, but greaternumbers are possible depending on the particular substituents selected.

It is well within the skill of the art to determine whether a particulargroup is electron donating or electron accepting. The most commonmeasure of electron donating and accepting properties is in terms ofHammett σ values. Hydrogen has a Hammett a value of zero, whileelectron-donating groups have negative Hammett σ values, andelectron-accepting groups have positive Hammett σ values. Lange'shandbook of Chemistry, 12^(th) Ed., McGraw-Hill, 1979, Table 3-12, pp.3-134 to 3-138, here incorporated by reference, lists Hammett σ valuesfor a large number of commonly encountered groups. Hammett σ values areassigned based on phenyl ring substitution, but they provide a practicalguide for qualitatively selecting electron donating and acceptinggroups.

Suitable electron-donating groups may be selected from —R′, —OR′, and—NR′(R″) where R′ is a hydrocarbon containing up to 6 carbon atoms andR″ is hydrogen or R′. Specific examples of electron-donating groupsinclude methyl, ethyl, phenyl, methoxy, ethoxy, phenoxy, —N(CH₃)₂,—N(CH₂CH₃)₂, —NHCH₃, —N(C₆H₅)₂, —N(CH₃)(C₆H₅), and —NHC₆H₅.

Suitable electron-accepting groups may be selected from the groupconsisting of cyano, α-haloalkyl, α-haloalkoxy, amido, sulfonyl,carbonyl, carbonyloxy and oxycarbonyl substituents containing up to 10carbon atoms. Specific examples include —CN, —F, —CF₃, —OCF₃, —CONHC₆H₅,—SO₂C₆H₅, —COC₆H₅, —CO₂C₆H₅, and —OCOC₆H₅.

For the purpose of this invention, also included in the definition of aheterocyclic ring are those rings that include coordinate or dativebonds. The definition of a coordinate bond can be found in Grant &Hackh's Chemical Dictionary, page 91. In essence, a coordinate bond isformed when electron-rich atoms such as O or N, donate a pair ofelectrons to electron-deficient atoms such as Al or B.

General Device Architecture

The present invention can be employed in many OLED device configurationsusing small molecule materials, oligomeric materials, polymericmaterials, or combinations thereof. These include very simple structurescomprising a single anode and cathode to more complex devices, such aspassive matrix displays comprised of orthogonal arrays of anodes andcathodes to form pixels, and active-matrix displays where each pixel iscontrolled independently, for example, with thin film transistors(TFTs).

There are numerous configurations of the organic layers wherein thepresent invention can be successfully practiced. The essentialrequirements of an OLED are an anode, a cathode, and an organiclight-emitting layer located between the anode and cathode. Additionallayers may be employed as more fully described hereafter.

A typical structure, especially useful for of a small molecule device,is shown in the FIGURE and is comprised of a substrate 101, an anode103, a hole-injecting layer 105, a hole-transporting layer 107, alight-emitting layer 109, a hole- or exciton-blocking layer 110, anelectron-transporting layer 111, and a cathode 113. These layers aredescribed in detail below. Note that the substrate may alternatively belocated adjacent to the cathode, or the substrate may actuallyconstitute the anode or cathode. The organic layers between the anodeand cathode are conveniently referred to as the organic EL element.Also, the total combined thickness of the organic layers is desirablyless than 500 nm.

The anode and cathode of the OLED are connected to a voltage/currentsource 150 through electrical conductors 160. The OLED is operated byapplying a potential between the anode and cathode such that the anodeis at a more positive potential than the cathode. Holes are injectedinto the organic EL element from the anode, and electrons are injectedinto the organic EL element at the cathode. Enhanced device stabilitycan sometimes be achieved when the OLED is operated in an AC mode where,for some time period in the cycle, the potential bias is reversed, andno current flows. An example of an AC driven OLED is described in U.S.Pat. No. 5,552,678.

Substrate

The OLED device of this invention is typically provided over asupporting substrate 101 where either the cathode or anode can be incontact with the substrate. The substrate can be a complex structurecomprising multiple layers of materials. This is typically the case foractive matrix substrates wherein TFTs are provided below the OLEDlayers. It is still necessary that the substrate, at least in theemissive pixelated areas, be comprised of largely transparent materials.The electrode in contact with the substrate is conveniently referred toas the bottom electrode. Conventionally, the bottom electrode is theanode, but this invention is not limited to that configuration. Thesubstrate can either be light transmissive or opaque, depending on theintended direction of light emission. The light-transmissive property isdesirable for viewing the EL emission through the substrate. Transparentglass or plastic is commonly employed in such cases. For applicationswhere the EL emission is viewed through the top electrode, thetransmissive characteristic of the bottom support can be lighttransmissive, light absorbing or light reflective. Substrates for use inthis case include, but are not limited to, glass, plastic, semiconductormaterials, silicon, ceramics, and circuit board materials. It isnecessary to provide in these device configurations a light-transparenttop electrode.

Anode

When the desired electroluminescent light emission (EL) is viewedthrough the anode, the anode 103 should be transparent or substantiallytransparent to the emission of interest. Common transparent anodematerials used in this invention are indium-tin oxide (ITO), indium-zincoxide (IZO), and tin oxide, but other metal oxides can work including,but not limited to, aluminum- or indium-doped zinc oxide,magnesium-indium oxide, and nickel-tungsten oxide. In addition to theseoxides, metal nitrides, such as gallium nitride, and metal selenides,such as zinc selenide, and metal sulfides, such as zinc sulfide, can beused as the anode. For applications where EL emission is viewed onlythrough the cathode, any conductive material can be used, transparent,opaque or reflective. Example conductors for this application include,but are not limited to, gold, iridium, molybdenum, palladium, andplatinum. Typical anode materials, transmissive or otherwise, have awork function of 4.1 eV or greater. Desired anode materials are commonlydeposited by any suitable means such as evaporation, sputtering,chemical vapor deposition, or electrochemical means. Anodes can bepatterned using well-known photolithographic processes. Optionally,anodes may be polished prior to application of other layers to reducesurface roughness so as to minimize shorts or enhance reflectivity.

Hole-Injecting Layer (HIL)

A hole-injecting layer 105 may be provided between the anode and thehole-transporting layer. The hole-injecting material can serve toimprove the film formation property of subsequent organic layers and tofacilitate injection of holes into the hole-transporting layer. Suitablematerials for use in the hole-injecting layer include, but are notlimited to, porphyrinic compounds as described in U.S. Pat. No.4,720,432, plasma-deposited fluorocarbon polymers as described in U.S.Pat. Nos. 6,127,004; 6,208,075; and 6,208,077, some aromatic amines, forexample, MTDATA(4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine), and inorganicoxides including vanadium oxide (VOx), molybdenum oxide (MoOx), andnickel oxide (NiOx). Alternative hole-injecting materials reportedlyuseful in organic EL devices are described in EP 0 891 121 A1 and EP 1029 909 A1.

The thickness of a hole-injection layer containing a plasma-depositedfluorocarbon polymer can be in the range of 0.2 nm to 15 nm and suitablyin the range of 0.3 to 1.5 nm.

Hole-Transporting Layer (HTL)

It is usually advantageous to have a hole-transporting layer 107deposited between the anode and the emissive layer. A hole-transportingmaterial deposited in said hole-transporting layer between the anode andthe light-emitting layer may be the same or different from ahole-transporting compound used as a co-host or in an exciton-blockinglayer according to the invention. The hole-transporting layer mayoptionally include a hole-injection layer. The hole-transporting layermay include more than one hole-transporting compound, deposited as ablend or divided into separate layers.

The hole-transporting layer contains at least one hole-transportingcompound such as an aromatic tertiary amine, where the latter isunderstood to be a compound containing at least one trivalent nitrogenatom that is bonded only to carbon atoms, at least one of which is amember of an aromatic ring. In one form the aromatic tertiary amine canbe an arylamine, such as a monoarylamine, diarylamine, triarylamine, ora polymeric arylamine. Exemplary monomeric triarylamines are illustratedby Klupfel et al. in U.S. Pat. No. 3,180,730. Other suitabletriarylamines substituted with one or more vinyl radicals and/orcomprising at least one active hydrogen containing group are disclosedby Brantly et al in U.S. Pat. Nos. 3,567,450 and 3,658,520.

A more preferred class of aromatic tertiary amines is those whichinclude at least two aromatic tertiary amine moieties as described inU.S. Pat. Nos. 4,720,432 and 5,061,569. Such compounds include thoserepresented by structural formula (HT1):

wherein:

Q₁ and Q₂ are independently selected aromatic tertiary amine moieties,and

G is a linking group such as an arylene, cycloalkylene, or alkylenegroup of a carbon to carbon bond.

In one embodiment, at least one of Q₁ or Q₂ contains a polycyclic fusedring structure, e.g., a naphthalene. When G is an aryl group, it isconveniently a phenylene, biphenylene, or naphthalene moiety.

A useful class of triarylamines satisfying structural formula (HT1) andcontaining two triarylamine moieties is represented by structuralformula (HT2):

wherein:

R₁ and R₂ each independently represents a hydrogen atom, an aryl group,or an alkyl group, or R₁ and R₂ together represent the atoms completinga cycloalkyl group; and

R₃ and R₄ each independently represents an aryl group, which is in turnsubstituted with a diaryl substituted amino group, as indicated bystructural formula (HT3):

wherein R₅ and R₆ are independently selected aryl groups. In oneembodiment, at least one of R₅ or R₆ contains a polycyclic fused ringstructure, e.g., a naphthalene.

Another class of aromatic tertiary amines is the tetraaryldiamines.Desirable tetraaryldiamines include two diarylamino groups, such asindicated by formula (HT3), linked through an arylene group. Usefultetraaryldiamines include those represented by formula (HT4):

wherein:

each Are is an independently selected arylene group, such as a phenyleneor anthracene moiety,

n is an integer of from 1 to 4, and

Ar, R₇, R₈, and R₉ are independently selected aryl groups.

In a typical embodiment, at least one of Ar, R₇, R₈, and R₉ is apolycyclic fused ring structure, e.g., a naphthalene.

The various alkyl, alkylene, aryl, and arylene moieties of the foregoingstructural formulae (HT1), (HT2), (HT3), (HT4) can each in turn besubstituted. Typical substituents include alkyl groups, alkoxy groups,aryl groups, aryloxy groups, and halide such as fluoride, chloride, andbromide. The various alkyl and alkylene moieties typically contain fromabout 1 to 6 carbon atoms. The cycloalkyl moieties can contain from 3 toabout 10 carbon atoms, but typically contain five, six, or seven ringcarbon atoms, such as cyclopentyl, cyclohexyl, and cycloheptyl ringstructures. The aryl and arylene moieties are usually phenyl andphenylene moieties.

The hole-transporting layer can be formed of a single tertiary aminecompound or a mixture of such compounds. Specifically, one may employ atriarylamine, such as a triarylamine satisfying the formula (HT2), incombination with a tetraaryldiamine, such as indicated by formula (HT4).Illustrative of useful aromatic tertiary amines are the following:

-   1,1-Bis(4-di-p-tolylaminophenyl)cyclohexane (TAPC);-   1,1-Bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane;-   N,N,N′,N′-tetraphenyl-4,4′″-diamino-1,1′:4′,1″:4′″-quaterphenyl;-   Bis(4-dimethylamino-2-methylphenyl)phenylmethane;-   1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene (BDTAPVB);-   N,N,N′,N′-Tetra-p-tolyl-4,4′-diaminobiphenyl;-   N,N,N′,N′-Tetraphenyl-4,4′-diaminobiphenyl;-   N,N,N′,N′-tetra-1-naphthyl-4,4′-diaminobiphenyl;-   N,N,N′,N′-tetra-2-naphthyl-4,4′-diaminobiphenyl;-   N-Phenylcarbazole;-   4,4′-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB);-   4,4′-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD);-   4,4′-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl (TNB);-   4,4′-Bis[N-(1-naphthyl)-N-phenylamino]p-terphenyl;-   4,4′-Bis[N-(2-naphthyl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(3-acenaphthenyl)-N-phenylamino]biphenyl;-   1,5-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene;-   4,4′-Bis[N-(9-anthryl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(1-anthryl)-N-phenylamino]-p-terphenyl;-   4,4′-Bis[N-(2-phenanthryl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(8-fluoranthenyl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(2-pyrenyl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(2-naphthacenyl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(2-perylenyl)-N-phenylamino]biphenyl;-   4,4′-Bis[N-(1-coronenyl)-N-phenylamino]biphenyl;-   2,6-Bis(di-p-tolylamino)naphthalene;-   2,6-Bis[di-(1-naphthyl)amino]naphthalene;-   2,6-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]naphthalene;-   N,N,N′,N′-Tetra(2-naphthyl)-4,4″-diamino-p-terphenyl;-   4,4′-Bis {N-phenyl-N-[4-(1-naphthyl)-phenyl]amino}biphenyl;-   2,6-Bis[N,N-di(2-naphthyl)amino]fluorine;-   4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine (MTDATA);-   N,N-bis[2,5-dimethyl-4-[(3-methylphenyl)phenylamino]phenyl]-2,5-dimethyl-N′-(3-methylphenyl)-N′-phenyl-1,4-benzenediamine;-   4-(9H-carbazol-9-yl)-N,N-bis[4-(9H-carbazol-9-yl)phenyl]-benzenamine    (TCTA);-   4-(3-phenyl-9H-carbazol-9-yl)-N,N-bis[4(3-phenyl-9H-carbazol-9-yl)phenyl]-benzenamine;-   9,9′-(2,2′-dimethyl[1,1′-biphenyl]-4,4′-diyl)bis-9H-carbazole    (CDBP);-   9,9′[1,1′-biphenyl]-4,4′-diylbis-9H-carbazole (CBP);-   9,9′-(1,3-phenylene)bis-9H-carbazole (mCP);-   9-[4-(9H-carbazol-9-yl)phenyl]-N,N-diphenyl-9H-carbazol-3-amine;-   9,9′-(1,4-phenylene)bis[N,N-diphenyl-9H-carbazol-3-amine;-   9-[4-(9H-carbazol-9-yl)phenyl]-N,N,N′,N′-tetraphenyl-9H-carbazole-3,6-diamine.

Another class of useful hole-transporting materials includes polycyclicaromatic compounds as described in EP 1 009 041. Some hole-injectingmaterials described in EP 0 891 121 A1 and EP 1 029 909 A1 can also makeuseful hole-transporting materials. In addition, polymerichole-transporting materials can be used including poly(N-vinylcarbazole)(PVK), polythiophenes, polypyrrole, polyaniline, and copolymersincluding poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) alsocalled PEDOT/PSS.

Exciton-Blocking Layer (EBL)

As described previously, an optional exciton- or electron-blocking layermay be present between the HTL and the LEL (not shown in the FIGURE).Some suitable examples of such blocking layers are described in U.S.Ser. No. 11/016,108 of Marina E. Kondavova et al., filed Dec. 17, 2004(now U.S. Pat. No. 7,597,967).

Light-Emitting Layer (LEL)

The light-emitting layer has been described previously. The device mayhave more than one light-emitting layer. Additional light-emittinglayers may include phosphorescent materials or fluorescent materials.The term “fluorescent” refers to a material that emits light from asinglet-excited state.

Fluorescent materials may be used in the same layer as thephosphorescent material, in adjacent layers, in adjacent pixels, or anycombination. Care must be taken to select materials that will notadversely affect the performance of the phosphorescent materials of thisinvention. One skilled in the art will understand that concentrationsand triplet energies of materials in the same layer as thephosphorescent material or in an adjacent layer must be appropriatelyset so as to prevent unwanted quenching of the phosphorescence.

As more fully described in U.S. Pat. Nos. 4,769,292 and 5,935,721, thelight-emitting layer (LEL) of the organic EL element includes aluminescent fluorescent or phosphorescent material whereelectroluminescence is produced as a result of electron-hole pairrecombination in this region. The light-emitting layer can be comprisedof a single material, but more commonly consists of a host materialdoped with a guest emitting material or materials where light emissioncomes primarily from the emitting materials and can be of any color. Thehost materials in the light-emitting layer can be anelectron-transporting material, as defined below, a hole-transportingmaterial, as defined above, or another material or combination ofmaterials that support hole-electron recombination. The emittingmaterial is usually chosen from highly fluorescent dyes andphosphorescent compounds, e.g., transition metal complexes as describedin WO 98/55561, WO 00/18851, WO 00/57676, and WO 00/70655. Emittingmaterials are typically incorporated at 0.01 to 10% by weight of thehost material.

The host and emitting materials can be small non-polymeric molecules orpolymeric materials such as polyfluorenes and polyvinylarylenes (e.g.,poly(p-phenylenevinylene), PPV). In the case of polymers, small moleculeemitting materials can be molecularly dispersed into a polymeric host,or the emitting materials can be added by copolymerizing a minorconstituent into a host polymer.

An important relationship for choosing an emitting material is acomparison of the bandgap potential which is defined as the energydifference between the highest occupied molecular orbital and the lowestunoccupied molecular orbital of the molecule. For efficient energytransfer from the host to the emitting material, a necessary conditionis that the band gap of the dopant is smaller than that of the hostmaterial. For phosphorescent emitters it is also important that the hosttriplet energy level be high enough to enable energy transfer from hostto emitting material.

Host and emitting materials known to be of use include, but are notlimited to, those disclosed in U.S. Pat. Nos. 4,769,292; 5,141,671;5,150,006; 5,151,629; 5,405,709; 5,484,922; 5,593,788; 5,645,948;5,683,823; 5,755,999; 5,928,802; 5,935,720; 5,935,721; and 6,020,078.

Metal complexes of 8-hydroxyquinoline and similar derivatives (FormulaE) constitute one class of useful host compounds capable of supportingelectroluminescence, and are particularly suitable for light emission ofwavelengths longer than 500 nm, e.g., green, yellow, orange, and red.

wherein:

M represents a metal;

n is an integer of from 1 to 4; and

Z independently in each occurrence represents the atoms completing anucleus having at least two fused aromatic rings.

From the foregoing it is apparent that the metal can be monovalent,divalent, trivalent, or tetravalent metal. The metal can, for example,be an alkali metal, such as lithium, sodium, or potassium; an alkalineearth metal, such as magnesium or calcium; an earth metal, such aluminumor gallium, or a transition metal such as zinc or zirconium. Generallyany monovalent, divalent, trivalent, or tetravalent metal known to be auseful chelating metal can be employed.

Z completes a heterocyclic nucleus containing at least two fusedaromatic rings, at least one of which is an azole or azine ring.Additional rings, including both aliphatic and aromatic rings, can befused with the two required rings, if required. To avoid addingmolecular bulk without improving on function the number of ring atoms isusually maintained at 18 or less.

Illustrative of useful chelated oxinoid compounds are the following:

-   CO-1: Aluminum trisoxine [alias, tris(8-quinolinolato)aluminum(III)]-   CO-2: Magnesium bisoxine [alias, bis(8-quinolinolato)magnesium(II)]-   CO-3: Bis[benzo {f}-8-quinolinolato]zinc (II)-   CO-4:    Bis(2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-8-quinolinolato)aluminum(III)-   CO-5: Indium trisoxine [alias, tris(8-quinolinolato)indium]-   CO-6: Aluminum tris(5-methyloxine) [alias,    tris(5-methyl-8-quinolinolato)aluminum(III)]-   CO-7: Lithium oxine [alias, (8-quinolinolato)lithium(I)]-   CO-8: Gallium oxine [alias, tris(8-quinolinolato)gallium(III)]-   CO-9: Zirconium oxine [alias, tetra(8-quinolinolato)zirconium(IV)]

Derivatives of anthracene (Formula F) constitute one class of usefulhost materials capable of supporting electroluminescence, and areparticularly suitable for light emission of wavelengths longer than 400nm, e.g., blue, green, yellow, orange, or red. Asymmetric anthracenederivatives as disclosed in U.S. Pat. No. 6,465,115 and WO 2004/018587are also useful hosts.

wherein:

R¹ and R² represent independently selected aryl groups, such asnaphthyl, phenyl, biphenyl, triphenyl, anthracene; and

R³ and R⁴ represent one or more substituents on each ring where eachsubstituent is individually selected from the following groups:

Group 1: hydrogen, or alkyl of from 1 to 24 carbon atoms;

Group 2: aryl or substituted aryl of from 5 to 20 carbon atoms;

Group 3: carbon atoms from 4 to 24 necessary to complete a fusedaromatic ring of anthracenyl, pyrenyl, or perylenyl;

Group 4: heteroaryl or substituted heteroaryl of from 5 to 24 carbonatoms as necessary to complete a fused heteroaromatic ring of furyl,thienyl, pyridyl, quinolinyl, or other heterocyclic systems;

Group 5: alkoxylamino, alkylamino, or arylamino of from 1 to 24 carbonatoms; and

Group 6: fluorine or cyano.

A useful class of anthracenes are derivatives of9,10-di-(2-naphthyl)anthracene (Formula G).

wherein R¹, R², R³, R⁴, R⁵, and R⁶ represent one or more substituents oneach ring where each substituent is individually selected from thefollowing groups:

Group 1: hydrogen, or alkyl of from 1 to 24 carbon atoms;

Group 2: aryl or substituted aryl of from 5 to 20 carbon atoms;

Group 3: carbon atoms from 4 to 24 necessary to complete a fusedaromatic ring of anthracenyl, pyrenyl, or perylenyl;

Group 4: heteroaryl or substituted heteroaryl of from 5 to 24 carbonatoms as necessary to complete a fused heteroaromatic ring of furyl,thienyl, pyridyl, quinolinyl, or other heterocyclic systems;

Group 5: alkoxylamino, alkylamino, or arylamino of from 1 to 24 carbonatoms; and

Group 6: fluorine or cyano.

Illustrative examples of anthracene materials for use in alight-emitting layer include:2-(4-methylphenyl)-9,10-di-(2-naphthyl)-anthracene;9-(2-naphthyl)-10-(1,1′-biphenyl)-anthracene;9,10-bis[4-(2,2-diphenylethenyl)phenyl]-anthracene;

Distyrylarylene derivatives are also useful hosts, as described in U.S.Pat. No. 5,121,029. Carbazole derivatives are particularly useful hostsfor phosphorescent emitters.

Useful fluorescent emitting materials include, but are not limited to,derivatives of anthracene, tetracene, xanthene, perylene, rubrene,coumarin, rhodamine, and quinacridone, dicyanomethylenepyran compounds,thiopyran compounds, polymethine compounds, pyrilium and thiapyriliumcompounds, fluorene derivatives, periflanthene derivatives,indenoperylene derivatives, bis(azinyl)amine boron compounds,bis(azinyl)methane compounds, and carbostyryl compounds. Illustrativeexamples of useful materials include, but are not limited to, thefollowing:

L1

L2

L3

L6

L4

L7

L5

L8

X R1 R2 L9  O H H L10 O H Methyl L11 O Methyl H L12 O Methyl Methyl L13O H t-butyl L14 O t-butyl H L15 O t-butyl t-butyl L16 S H H L17 S HMethyl L18 S Methyl H L19 S Methyl Methyl L20 S H t-butyl L21 S t-butylH L22 S t-butyl t-butyl

X R1 R2 L23 O H H L24 O H Methyl L25 O Methyl H L26 O Methyl Methyl L27O H t-butyl L28 O t-butyl H L29 O t-butyl t-butyl L30 S H H L31 S HMethyl L32 S Methyl H L33 S Methyl Methyl L34 S H t-butyl L35 S t-butylH L36 S t-butyl t-butyl

R L37 phenyl L38 methyl L39 t-butyl L40 mesityl

R L41 phenyl L42 methyl L43 t-butyl L44 mesityl

L45

L46

L47

L48

L49

L50

L51

L52

L53

L54

In addition to the phosphorescent materials of Formula (1), additionalphosphorescent materials may be present in the same or a differentlayer. Examples of other phosphorescent materials are reported in WO00/57676, WO 00/70655, WO 01/39234, WO 01/41512, WO 01/93642, WO02/15645, WO 02/71813, WO 02/74015, EP 1 238 981, EP 1 239 526, EP 1 244155, U.S. 2002/0100906, JP 2003-073387, JP 2003-073388 (with counterpartU.S. 2003/0152802), JP 2003-059667 (with counterpart U.S. 2004/0239237),JP 2003-073665, U.S. 2002/0121638, U.S. 2002/0197511, U.S. 2003/0017361,U.S. 2003/0040627, U.S. 2003/0054198, U.S. 2003/0059646, U.S.2003/0068526, U.S. 2003/0068528, U.S. 2003/0068535, U.S. 2003/0072964,U.S. 2003/0124381, U.S. 2003/0141809, and U.S. Pat. Nos. 6,097,147;6,413,656; 6,451,415; 6,451,455; 6,458,475; 6,515,298; and 6,573,651.

The emission wavelengths of cyclometallated Ir(III) complexes of thetype IrL₃ and IrL₂L′, such as the green-emittingfac-tris(2-phenylpyridinato-N,C²′)Iridium(III) andbis(2-phenylpyridinato-N,C²′)Iridium(III)(acetylacetonate), may beshifted by substitution of electron donating or withdrawing groups atappropriate positions on the cyclometallating ligand L, or by choice ofdifferent heterocycles for the cyclometallating ligand L. The emissionwavelengths may also be shifted by choice of the ancillary ligand L′.Examples of red emitters are thebis(2-(2′-benzothienyl)pyridinato-N,C³′)Iridium(III)(acetylacetonate)and tris(2-phenylisoquinolinato-N,C)Iridium(III). A blue-emittingexample isbis(2-(4,6-diflourophenyl)-pyridinato-N,C²′)Iridium(III)(picolinate).

Other important phosphorescent materials include cyclometallated Pt(II)complexes such as cis-bis(2-phenylpyridinato-N,C²′)platinum(II),cis-bis(2-(2′-thienyl)pyridinato-N,C³′) platinum(II),cis-bis(2-(2′-thienyl)quinolinato-N,C⁵′) platinum(II), or(2-(4,6-diflourophenyl)pyridinato-N,C²′) platinum (II) acetylacetonate.Pt(II) porphyrin complexes such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II) are also useful phosphorescent materials.

Still other examples of useful phosphorescent materials includecoordination complexes of the trivalent lanthanides such as Tb³⁺ andEu³⁺ (J. Kido et al., Appl. Phys. Lett., 65, 2124 (1994)).

Hole-Blocking Layer (HBL)

As described previously, in addition to suitable hosts and transportingmaterials, an OLED device according to the invention may also include atleast one hole-blocking layer 110 placed between theelectron-transporting layer 111 and the light-emitting layer 109 to helpconfine the excitons and recombination events to the light-emittinglayer comprising hosts or co-hosts and a phosphorescent emitter. In thiscase, there should be an energy barrier for hole migration from hosts orco-hosts into the hole-blocking layer, while electrons should passreadily from the hole-blocking layer into the light-emitting layercomprising host or co-host materials and a phosphorescent emitter. Thefirst requirement entails that the ionization potential of thehole-blocking layer 110 be larger than that of the light-emitting layer109, desirably by 0.2 eV or more. The second requirement entails thatthe electron affinity of the hole-blocking layer 110 not greatly exceedthat of the light-emitting layer 109, and desirably be either less thanthat of light-emitting layer or not exceed that of the light-emittinglayer by more than about 0.2 eV.

When used with an electron-transporting layer whose characteristicluminescence is green, such as an Alq-containing electron-transportinglayer as described below, the requirements concerning the energies ofthe highest occupied molecular orbital (HOMO) and lowest unoccupiedmolecular orbital (LUMO) of the material of the hole-blocking layerfrequently result in a characteristic luminescence of the hole-blockinglayer at shorter wavelengths than that of the electron-transportinglayer, such as blue, violet, or ultraviolet luminescence. Thus, it isdesirable that the characteristic luminescence of the material of ahole-blocking layer be blue, violet, or ultraviolet. It is furtherdesirable that the triplet energy of the hole-blocking material begreater than that of the phosphorescent material. Suitable hole-blockingmaterials are described in WO 00/70655A2, WO 01/41512 and WO 01/93642A1. Two examples of useful hole-blocking materials are bathocuproine(BCP) and bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(BAlq). The characteristic luminescence of BCP is in the ultraviolet,and that of BAlq is blue. Metal complexes other than BAlq are also knownto block holes and excitons as described in U.S. 2003/0068528. When ahole-blocking layer is used, its thickness can be between 2 and 100 nm,and suitably between 5 and 10 nm.

Electron-Transporting Layer (ETL)

The electron-transporting material deposited in saidelectron-transporting layer between the cathode and the light-emittinglayer may be the same or different from an electron-transporting host orco-host material. The electron-transporting layer may include more thanone electron-transporting compound, deposited as a blend or divided intoseparate layers.

Preferred thin film-forming materials for use in constructing theelectron-transporting layer of the organic EL devices of this inventionare metal-chelated oxinoid compounds, including chelates of oxine itself(also commonly referred to as 8-quinolinol or 8-hydroxyquinoline). Suchcompounds help to inject and transport electrons, exhibiting high levelsof performance, and are readily fabricated in the form of thin films.Exemplary of contemplated oxinoid compounds are those satisfyingstructural formula (ET1) below:

wherein:

M represents a metal;

n is an integer of from 1 to 4; and

Z independently in each occurrence represents the atoms completing anucleus having at least two fused aromatic rings.

From the foregoing it is apparent that the metal can be monovalent,divalent, trivalent, or tetravalent metal. The metal can, for example,be an alkali metal, such as lithium, sodium, or potassium; an alkalineearth metal, such as magnesium or calcium; an earth metal, such aluminumor gallium; or a transition metal such as zinc or zirconium. Generallyany monovalent, divalent, trivalent, or tetravalent metal known to be auseful chelating metal can be employed.

Z completes a heterocyclic nucleus containing at least two fusedaromatic rings, at least one of which is an azole or azine ring.Additional rings, including both aliphatic and aromatic rings, can befused with the two required rings, if required. To avoid addingmolecular bulk without improving on function the number of ring atoms isusually maintained at 18 or less.

Illustrative of useful chelated oxinoid compounds are the following:

-   CO-1: Aluminum trisoxine [alias,    tris(8-quinolinolato)aluminum(III)];-   CO-2: Magnesium bisoxine [alias, bis(8-quinolinolato)magnesium(II)];-   CO-3: Bis[benzo{f}-8-quinolinolato]zinc (II);-   CO-4:    Bis(2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-8-quinolinolato)aluminum(III);-   CO-5: Indium trisoxine [alias, tris(8-quinolinolato)indium];-   CO-6: Aluminum tris(5-methyloxine) [alias,    tris(5-methyl-8-quinolinolato)aluminum(III)];-   CO-7: Lithium oxine [alias, (8-quinolinolato)lithium(I)];-   CO-8: Gallium oxine [alias, tris(8-quinolinolato)gallium(III)];-   CO-9: Zirconium oxine [alias, tetra(8-quinolinolato)zirconium(IV)].

Other electron-transporting materials suitable for use in theelectron-transporting layer include various butadiene derivatives asdisclosed in U.S. Pat. No. 4,356,429 and various heterocyclic opticalbrighteners as described in U.S. Pat. No. 4,539,507. Benzazolessatisfying structural formula (ET2) are also usefulelectron-transporting materials:

wherein:

n is an integer of 3 to 8;

Z is O, NR or S;

R and R′ are individually hydrogen; alkyl of from 1 to 24 carbon atoms,for example, propyl, t-butyl, heptyl, and the like; aryl or hetero-atomsubstituted aryl of from 5 to 20 carbon atoms for example phenyl andnaphthyl, furyl, thienyl, pyridyl, quinolinyl and other heterocyclicsystems; or halo such as chloro, fluoro; or atoms necessary to completea fused aromatic ring; and

X is a linkage unit consisting of carbon, alkyl, aryl, substitutedalkyl, or substituted aryl, which conjugately or unconjugately connectsthe multiple benzazoles together.

An example of a useful benzazole is2,2′,2″-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole] (TPBI)disclosed in Shi et al. in U.S. Pat. No. 5,766,779.

Other electron-transporting materials suitable for use in theelectron-transporting layer 111 include various butadiene derivatives asdisclosed in U.S. Pat. No. 4,356,429 and various heterocyclic opticalbrighteners as described in U.S. Pat. No. 4,539,507. Benzazolessatisfying structural formula (G) are also useful electron-transportingmaterials. Triazines are also known to be useful aselectron-transporting materials. Further useful materials aresilacyclopentadiene derivatives described in EP 1 480 280, EP 1 478 032,and EP 1 469 533. Substituted 1,10-phenanthroline compounds such as

are disclosed in JP2001-267080, JP2003-115387, JP2004-311184, and WO02/43449. Pyridine derivatives are described in JP2004-200162 as usefulelectron-transporting materials.

In one embodiment, the electron-transporting layer includes a mixture ofmaterials such as those described by W. Begley et al. in U.S. Ser. No.11/076,821 filed Mar. 10, 2005 (now abandoned); U.S. Ser. No. 11/077,218filed Mar. 10, 2005 (published as U.S. 2006/0204784); and U.S. Ser. No.11/116,096 filed Apr. 27, 2005 (published as U.S. 2006/0246315), thedisclosures of which are incorporated herein by reference.

If both a hole-blocking layer and an electron-transporting layer 111 areused, electrons should pass readily from the electron-transporting layer111 into the hole-blocking layer. Therefore, the electron affinity ofthe electron-transporting layer 111 should not greatly exceed that ofthe hole-blocking layer. Desirably, the electron affinity of theelectron-transporting layer should be less than that of thehole-blocking layer or not exceed it by more than about 0.2 eV.

If an electron-transporting layer is used, its thickness may be between2 and 100 nm, and suitably between 5 and 20 nm.

Electron-Injecting Layer (EIL)

Electron-injecting layers (not shown in the FIGURE), when present,include those described in U.S. Pat. Nos. 5,608,287; 5,776,622;5,776,623; 6,137,223; and 6,140,763, the disclosures of which areincorporated herein by reference. An electron-injecting layer generallyconsists of a material having a work function less than 4.0 eV. Athin-film containing low work-function alkaline metals or alkaline earthmetals, such as Li, Cs, Ca, Mg can be employed. In addition, an organicmaterial doped with these low work-function metals can also be usedeffectively as the electron-injecting layer. Examples are Li- orCs-doped Alq. In one suitable embodiment the electron-injecting layerincludes LiF. In practice, the electron-injecting layer is often a thinlayer deposited to a suitable thickness in a range of 0.1-3.0 nm.

Cathode

When light emission is viewed solely through the anode 103, the cathodeused in this invention can be comprised of nearly any conductivematerial. Desirable materials have good film-forming properties toensure good contact with the underlying organic layer, promote electroninjection at low voltage, and have good stability. Useful cathodematerials often contain a low work function metal (<4.0 eV) or metalalloy. One useful cathode material is comprised of a Mg:Ag alloy whereinthe percentage of silver is in the range of 1 to 20%, as described inU.S. Pat. No. 4,885,211. Another suitable class of cathode materialsincludes bilayers comprising a thin electron-injection layer (EIL) incontact with an organic layer (e.g., an electron-transporting layer(ETL)) which is capped with a thicker layer of a conductive metal. Here,the EIL preferably includes a low work function metal or metal salt, andif so, the thicker capping layer does not need to have a low workfunction. One such cathode is comprised of a thin layer of LiF followedby a thicker layer of Al as described in U.S. Pat. No. 5,677,572. An ETLmaterial doped with an alkali metal, for example, Li-doped Alq, asdisclosed in U.S. Pat. No. 6,013,384, is another example of a usefulEIL. Other useful cathode material sets include, but are not limited to,those disclosed in U.S. Pat. Nos. 5,059,861; 5,059,862; and 6,140,763.

When light emission is viewed through the cathode, the cathode must betransparent or nearly transparent. For such applications, metals must bethin or one must use transparent conductive oxides, or a combination ofthese materials. Optically transparent cathodes have been described inmore detail in U.S. Pat. Nos. 4,885,211; 5,247,190; 5,608,287;5,677,572; 5,703,436; 5,714,838; 5,739,545; 5,776,622; 5,776,623;5,837,391; 5,969,474; 5,981,306; 6,137,223; 6,140,763; 6,172,459;6,278,236; and 6,284,393; and in EP 1 076 368 and JP 3,234,963. Cathodematerials are typically deposited by any suitable methods such asevaporation, sputtering, or chemical vapor deposition. When needed,patterning can be achieved through many well-known methods including,but not limited to, through-mask deposition, integral shadow masking asdescribed in U.S. Pat. No. 5,276,380 and EP 0 732 868, laser ablation,and selective chemical vapor deposition.

Other Common Organic Layers and Device Architecture

In some instances, layers 109 and 111 can optionally be collapsed into asingle layer that serves the function of supporting both light emissionand electron transportation. It also known in the art that emittingdopants may be added to the hole-transporting layer, which may serve asa host. Multiple dopants may be added to one or more layers in order tocreate a white-emitting OLED, for example, by combining blue- andyellow-emitting materials, cyan- and red-emitting materials, or red-,green-, and blue-emitting materials. White-emitting devices aredescribed, for example, in EP 1 182 244, EP 1 187 235, U.S.2002/0186214, U.S. 2002/0025419, U.S. 2004/0009367, and U.S. Pat. Nos.5,283,132; 5,405,709; 5,503,910; 5,683,823; and 6,627,333.

Additional layers such as exciton-, electron- and hole-blocking layersas taught in the art may be employed in devices of this invention.Hole-blocking layers are commonly used to improve efficiency ofphosphorescent emitter devices, for example, as in WO 00/70655 A2, WO01/93642 A1, U.S. 2002/0015859, U.S. 2003/0068528, and U.S. 2003/0175553A1.

This invention may be used in so-called stacked device architecture, forexample, as taught in U.S. Pat. Nos. 5,703,436 and 6,337,492.

Deposition of Organic Layers

The organic materials mentioned above are suitably deposited through avapor-phase method such as sublimation, but can be deposited from afluid, for example, from a solvent with an optional binder to improvefilm formation. If the material is a polymer, solvent deposition isuseful but other methods can be used, such as sputtering or thermaltransfer from a donor sheet. The material to be deposited by sublimationcan be vaporized from a sublimation “boat” often comprised of a tantalummaterial, e.g., as described in U.S. Pat. No. 6,237,529, or can be firstcoated onto a donor sheet and then sublimed in closer proximity to thesubstrate. Layers with a mixture of materials can utilize separatesublimation boats, or the materials can be pre-mixed and coated from asingle boat or donor sheet. Patterned deposition can be achieved usingshadow masks, integral shadow masks (U.S. Pat. No. 5,294,870),spatially-defined thermal dye transfer from a donor sheet (U.S. Pat.Nos. 5,688,551; 5,851,709; and 6,066,357) and inkjet method (U.S. Pat.No. 6,066,357).

One preferred method for depositing the materials of the presentinvention is described in U.S. 2004/0255857 and U.S. Ser. No. 10/945,941(now U.S. Pat. No. 7,288,286) where different source evaporators areused to evaporate each of the materials of the present invention. Asecond preferred method involves the use of flash evaporation wherematerials are metered along a material feed path in which the materialfeed path is temperature controlled. Such a preferred method isdescribed in the following co-assigned patent applications: U.S. Ser.Nos. 10/784,585; 10/805,980; 10/945,940; 10/945,941; 11/050,924; and11/050,934 (now U.S. Pat. Nos. 7,232,588; 7,238,389; 7,288,285;7,288,286; 7,625,601; and 7,165,340 respectively). Using this secondmethod, each material may be evaporated using different sourceevaporators, or the solid materials may be mixed prior to evaporationusing the same source evaporator.

Encapsulation

Most OLED devices are sensitive to moisture or oxygen, or both, so theyare commonly sealed in an inert atmosphere such as nitrogen or argon. Insealing an OLED device in an inert environment, a protective cover canbe attached using an organic adhesive, a metal solder, or a low meltingtemperature glass. Commonly, a getter or desiccant is also providedwithin the sealed space. Useful getters and desiccants include alkaliand alkaline metals, alumina, bauxite, calcium sulfate, clays, silicagel, zeolites, alkaline metal oxides, alkaline earth metal oxides,sulfates, or metal halides and perchlorates. Methods for encapsulationand desiccation include, but are not limited to, those described in U.S.Pat. No. 6,226,890. In addition, barrier layers such as SiOx, Teflon,and alternating inorganic/polymeric layers are known in the art forencapsulation.

Optical Optimization

OLED devices of this invention can employ various well-known opticaleffects in order to enhance its properties if desired. This includesoptimizing layer thicknesses to yield maximum light transmission,providing dielectric minor structures, replacing reflective electrodeswith light-absorbing electrodes, providing anti-glare or anti-reflectioncoatings over the display, providing a polarizing medium over thedisplay, or providing colored, neutral density, or color conversionfilters in functional relationship with the light-emitting areas of thedisplay. Filters, polarizers, and anti-glare or anti-reflection coatingscan also be provided over a cover or as part of a cover.

The OLED device may have a microcavity structure. In one useful example,one of the metallic electrodes is essentially opaque and reflective; theother one is reflective and semitransparent. The reflective electrode ispreferably selected from Au, Ag, Mg, Ca, or alloys thereof. Because ofthe presence of the two reflecting metal electrodes, the device has amicrocavity structure. The strong optical interference in this structureresults in a resonance condition. Emission near the resonance wavelengthis enhanced, and emission away from the resonance wavelength isdepressed. The optical path length can be tuned by selecting thethickness of the organic layers, or by placing a transparent opticalspacer between the electrodes. For example, an OLED device of thisinvention can have ITO spacer layer placed between a reflective anodeand the organic EL media, with a semitransparent cathode over theorganic EL media.

The entire contents of the patents and other publications referred to inthis specification are incorporated herein by reference.

Embodiments of the invention may provide advantageous features such ashigher luminous yield, lower drive voltage, and higher power efficiency,longer operating lifetimes, or ease of manufacture. Embodiments ofdevices useful in the invention can provide a wide range of huesincluding those useful in the emission of white light (directly orthrough filters to provide multicolor displays). Embodiments of theinvention can also provide an area lighting device.

The invention and its advantages are further illustrated by the specificexamples that follow. Unless otherwise specified, the term “percentage”or “percent” and the symbol “%” of a material indicate the volumepercent of the material in the layer in which it is present.

Example 1 Synthesis of Inv-1,fac-tris(2-phenylquinazolinato-N,C²′)iridium(III)

K₃IrBr₆ (2.80 g, 3.55 mmol) was placed in a 200 mL round bottom flaskwith 45 mL of 2-ethoxyethanol, 15 mL water, and 2-phenylquinazoline(8.87 mmol). The mixture was freeze-thaw degassed, and then refluxed for4 h under nitrogen atmosphere during which time an orange precipitateappeared. After cooling, the precipitate was collected by filtration,washed with 1N HBr(aq), then water, then ethanol, and dried to yieldorange tetrakis(2-phenylquinazolinato-N,C²′)(μ-dibromo)diiridium(III)(2.29 g, 94% yield based on iridium).

Then tetrakis(2-phenylquinazolinato-N,C²′)(μ-dibromo)diiridium(III)(0.85 g, 1.245 mmol) and silver tetrafluoroborate (0.27 g) were placedin a 100-mL round-bottomed flask. Acetonitrile (30 mL) was added and themixture was freeze-thaw degassed, and then refluxed for 3 h undernitrogen atmosphere. After cooling, the yellow solution was filteredthrough celite filter aid to remove white insoluble material, and thesolvent was removed under vacuum. A yellow powder was collected, anddried to afford[bis(acetonitrile)bis(2-phenylquinazolinato-N,C²′)iridium(III)]tetrafluoroborate(0.953 g, 99% based on iridium). Analysis by H¹ NMR spectroscopy andmass spectrometry confirmed that this material wasbis(acetonitrile)bis[(2-phenylpyridinato-N,C²′)]iridium(III)tetrafluoroborate.

Next, [bis(acetonitrile)bis(2-phenylquinazolinato-N,C²′)iridium(III)]tetrafluoroborate (0.615 g,0.797 mmol) and 2-phenylquinazoline (0.71 g) was placed in a 100-mLround-bottomed flask with 2-ethoxyethanol (30 mL). The mixture wasfreeze-thaw degassed, and then refluxed for 18 h under nitrogenatmosphere during which time a bright orange precipitate appeared. Aftercooling, the precipitate was collected by filtration, washed withethanol and water, and dried to affordfac-tris(2-phenylquinazolinato-N,C²′)iridium(III) (0.433 g, 67.3%yield). Analysis by electrospray mass spectrometry (M+ observed 807 amu)and 1H NMR spectroscopy confirmed the identity of the product.

Example 2 Synthesis of Inv-2, offac-tris(4-phenylquinazolinato-N,C²′)iridium(III)

K₃IrBr₆ (2.755 g, 3.49 mmol) was placed in a 125 mL round bottom flaskwith 39 mL of 2-ethoxyethanol, 13 mL water, and 4-phenylquinazoline(1.80 g, 8.73 mmol). The mixture was freeze-thaw degassed, and thenrefluxed for 4 h under nitrogen atmosphere during which time a dark redprecipitate appeared. After cooling, the precipitate was collected byfiltration, washed with methanol and ligroin, and dried to yield darkred tetrakis(4-phenylquinazolinato-N,C²′)(μ-dibromo)diiridium(III)(2.265 g, 95% yield based on iridium).

Next, tetrakis(4-phenylquinazolinato-N,C²′)(μ-dibromo)diiridium(III)(0.696 g, 1.02 mmol) and silver tetrafluoroborate (0.218 g) were placedin a 100-mL round-bottom flask. Acetonitrile (30 mL) was added and themixture was freeze-thaw degassed, and then refluxed for 3 h undernitrogen atmosphere. After cooling, the red-orange solution was filteredthrough celite filter aid to remove white insoluble material, and thenthe solvent was removed under vacuum. A red-orange was collected, anddried to afford [bis(acetonitrile)bis(4-phenylquinazolinato-N,C²′)iridium(III)]tetrafluoroborate (0.759 g,96% based on iridium). Analysis by H¹ NMR spectroscopy and massspectrometry confirmed that this material wasbis(acetonitrile)bis[(4-phenylpyridinato-N,C²′)]iridium(III)tetrafluoroborate.

Then[bis(acetonitrile)bis(4-phenylquinazolinato-N,C²′)iridium(III)]tetrafluoroborate(0.497 g, 0.644 mmol) and 4-phenylquinazoline (0.53 g) was placed in a100-mL round-bottom flask with 2-ethoxyethanol (30 mL). The mixture wasfreeze-thaw degassed, and then refluxed for 18 h under nitrogenatmosphere during which time a dark red precipitate appeared. Aftercooling, the precipitate was collected by filtration, washed withethanol and water, and dried to affordfac-tris(4-phenylquinazolinato-N,C²′)iridium(III) (0.375 g, 72% yield).Analysis by electrospray mass spectrometry (M+ observed 807 amu) and ¹HNMR spectroscopy confirmed the identity of the product.

Example 3 Fabrication of Devices 1-1 Through 1-3

An EL device (1-1) satisfying the requirements of the invention wasconstructed in the following manner:

A glass substrate coated with an 85 nm layer of indium-tin oxide (ITO)as the anode was sequentially ultrasonicated in a commercial detergent,rinsed in deionized water, degreased in toluene vapor, and exposed tooxygen plasma for about 1 min.

a) Over the ITO was deposited a 1 nm fluorocarbon (CFx) hole-injectinglayer (HIL) by plasma-assisted deposition of CHF₃.

b) A hole-transporting layer (HTL) ofN,N′-di-1-naphthalenyl-N,N′-diphenyl-4,4′-diaminobiphenyl (NPB) having athickness of 150 nm was then evaporated from a tantalum boat.

c) A 35 nm LEL comprised of CBP (4,4′-N,N′-dicarbazole-biphenyl) and 4wt % of the phosphorescent dopant Inv-1 were then deposited onto thehole-transporting layer. These materials were also evaporated fromgraphite boats.

d) A 10 nm hole-blocking layer of bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (BAlq) was deposited onto the LEL. Thismaterial was also evaporated from a graphite boat.

e) A 40 nm electron-transporting layer (ETL) oftris(8-quinolinolato)aluminum (III) (Alq₃) was then deposited onto thelight-emitting layer. This material was also evaporated from a graphiteboat.

f) On top of the Alg₃ layer was deposited a 220 nm cathode formed of a10:1 volume ratio of Mg and Ag.

The above sequence completed the deposition of the EL device. The devicewas then hermetically packaged in a dry glove box for protection againstambient environment. Devices 1-2 and 1-3 were constructed in exactly thesame manner as Device 1-1, except the level of Inv-1 was 6% and 8%respectively.

The cells thus formed were tested at 20 mA/cm² constant current forefficiency in the form of luminance yield (Cd/A) and radiant yield (W/A)where radiant yield is the radiant flux (in watts) produced by thedevice per ampere of input current, where radiant flux is the lightenergy produced by the device per unit time. Testing also determined theoutput color, reported in CIEx, CIEy (Commission Internationale del'Eclairage) coordinates and drive voltage. The results are listed inTable 1a and 1b.

The stability of the devices was also measured by operating the devicesfor 430 hrs at a current density of 20 mA/cm² and ambient temperature(˜23° C.). The percent of luminance remaining after this time periodrelative to the initial luminance is listed in Table 1b as a percentage.

TABLE 1a Testing data for Devices 1-1, 1-2, 1-3. Luminance Inv-1 ColorEmission Yield Device Level (%) CIEx, y λ_(max) (nm) (cd/A)¹ 1-1 40.548, 0.424 603 4.66 1-2 6 0.561, 0.415 608 4.50 1-3 8 0.563, 0.413 6104.17 ¹at 20 mA/cm²

TABLE 1b Testing data for Devices 1-1, 1-2, 1-3. Inv-1 Drive VoltageRadiant Stability² Device Level (%) (V) ¹ Yield (%) 1-1 4 11.4 0.05180.2% 1-2 6 11.2 0.053 79.3% 1-3 8 10.6 0.051 78.3% ¹ at 20 mA/cm²²Percent luminance remaining after 430 hours of operation.

From the data presented in Table 1a and 1b, it can be seen that thedevices according to the invention provide high luminance yield withhigh color purity and good stability.

Example 4 Fabrication of Devices 2-1 Through 2-3

Devices 2-1, 2-2, and 2-3 were fabricated in exactly the same manner asDevice 1-1, 1-2, and 1-3 described above, except Inv-1 was replaced withInv-2 in each case. The devices were tested in the same manner as thosein Example 3, and the results are listed in Table 2a and 2b.

TABLE 2a Testing data for Devices 2-1, 2-2, 2-3. Luminance Inv-2 ColorEmission Yield Device Level (%) CIE x, y λ_(max) (nm) (cd/A)¹ 2-1 40.577, 0.388 634 3.38 2-2 6 0.580, 0.385 637 3.15 2-3 8 0.583, 0.383 6393.20 ¹at 20 mA/cm²

TABLE 2b Testing data for Devices 2-1, 2-2, 2-3. Inv-2 Drive VoltageRadiant Stability² Device Level (%) (V) ¹ Yield (%) 2-1 4 11.2 0.06180.2% 2-2 6 11.2 0.062 79.3% 2-3 8 10.6 0.065 78.3% ¹ at 20 mA/cm²²Percent luminance remaining after 430 hours of operation.

As can be seen from Table 2a and 2b, devices prepared according to theinvention provide high luminance yield with high color purity and goodstability.

Example 5 Fabrication of Devices 3-1 Through 3-6

EL devices satisfying the requirements of the invention were constructedin the following manner:

A glass substrate coated with an 85 nm layer of indium-tin oxide (ITO)as the anode was sequentially ultrasonicated in a commercial detergent,rinsed in deionized water, degreased in toluene vapor, and exposed tooxygen plasma for about 1 min.

a) Over the ITO was deposited a 1 nm fluorocarbon (CFx) hole-injectinglayer (HIL) by plasma-assisted deposition of CHF₃.

b) A hole-transporting layer (HTL) ofN,N′-di-1-naphthalenyl-N,N′-diphenyl-4,4′-diaminobiphenyl (NPB) having athickness of 150 nm was then evaporated from a tantalum boat.

c) A 35 nm LEL comprised of the co-hosts PH-10 and NPB and thephosphorescent dopant Inv-2 were then deposited onto thehole-transporting layer. See Table 3a for the levels of each of thesecomponents. These materials were also evaporated from graphite boats.

d) A 10 nm hole-blocking layer of PH-10 was deposited onto the LEL.

e) A 40 nm electron-transporting layer (ETL) oftris(8-quinolinolato)aluminum (III) (Alq₃) was then deposited onto thelight-emitting layer. This material was also evaporated from a graphiteboat.

f) On top of the Alq₃ layer was deposited a 220 nm cathode formed of a10:1 volume ratio of Mg and Ag.

The above sequence completed the deposition of the EL device. The devicewas then hermetically packaged in a dry glove box for protection againstambient environment.

TABLE 3a Components used in the LEL. Device PH-10 Wt % NPB Wt % Inv-2 Wt% 3-1 83 15 2 3-2 81 15 4 3-3 76 20 4 3-4 66 30 4 3-5 74 20 6 3-6 94  06

The cells thus formed were tested at 0.5 mA/cm² constant current forefficiency in the form of luminance yield (Cd/A) and radiant yield(W/A). Testing was also determined the output color reported in CIEx,CIEy coordinates and drive voltage. The results are listed in Table 3b.

The stability of the devices was also measured by operating the devicesfor 474 hrs at a current density of 20 mA/cm². The percent of luminanceremaining after this time period is listed in Table 3b.

TABLE 3b Testing data for Devices 3-1 through 3-6. Luminance DriveEmission Radi- Stabil- De- Color Yield Voltage λ_(max) ant ity² viceCIEx, y (cd/A)¹ (V)¹ (nm) Yield (%) 3-1 0.661, 0.323 5.27 7.2 636 0.13687 3-2 0.673, 0.319 4.50 7.2 639 0.131 86 3-3 0.673, 0.318 4.68 6.3 6390.135 87 3-4 0.674, 0.316 5.07 5.6 638 0.142 84 3-5 0.678, 0.315 4.256.4 641 0.135 87 3-6 0.612, 0.362 2.52 8.5 645 0.066 82 ¹Measured at 0.5mA/cm² constant current. ²Percent luminance remaining after 474 hours ofoperation.

It can be seen from Table 3b, that the inventive devices offer highluminance and excellent stability. In addition, if one compares Devices3-1 through 3-5, which have a host material that is a mixture of PH-10and NPB, with Device 3-6 which has only a single host (PH-10), one cansee that the mixed host in combination with the dopant of Formula (1)offers a significant improvement in luminance yield, efficiency, andstability, as well as reduced drive voltage.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

The patents and other publications referred to are incorporated hereinin their entirety.

PARTS LIST

-   101 Substrate-   103 Anode-   105 Hole-Injecting layer (HIL)-   107 Hole-Transporting layer (HTL)-   109 Light-Emitting layer (LEL)-   110 Hole-Blocking Layer (HBL)-   111 Electron-Transporting layer (ETL)-   113 Cathode-   150 Voltage/Current Source-   160 Electrical Connectors

We claim:
 1. An OLED device comprising a cathode, an anode, and locatedtherebetween a light-emitting layer containing a) atris-ĈN-cyclometallated complex represented by Formula (2c)

wherein: each d¹ represents an independently selected substituent and sis 0-4; each d² represents an independently selected substituent and tis 0-4; and d³ represents hydrogen or a substituent; b) anelectron-transporting host material, and c) a hole-transporting hostmaterial.
 2. The OLED device of claim 1, wherein theelectron-transporting host is a complex represented by Formula (PH-10)


3. The OLED device of claim 1, wherein the hole-transporting host isN,N′-di-1-naphthalenyl-N,N′-diphenyl-4,4′-diaminobiphenyl.
 4. The OLEDdevice of claim 1, wherein the tris-ĈN-cyclometallated complex is


5. A tris-ĈN-cyclometallated complex represented by Formula (2c)

wherein: each d¹ represents an independently selected substituent and sis 0-4; each d² represents an independently selected substituent and tis 0-4; and d³ represents hydrogen or a substituent.
 6. Thetris-ĈN-cyclometallated complex